1. Field of the Invention
The present invention relates to an antenna device and more particularly to the antenna device that can operate in a plurality of frequency bands and a wireless communication device using the antenna device.
2. Description of the Related Art
In recent years, a wireless communication apparatus such as a mobile phone or a like has become widespread and various bands of frequencies are used in communications.
In a recently-available mobile phone called a dual-band, triple-band, or quad-band type mobile phone in particular, one mobile phone is made to operate in a plurality of transmitting and receiving frequency bands.
In such a circumstance, hurried development of an antenna device making up antenna circuits embedded in a mobile phone or a like being capable of operating in the plurality of transmitting and receiving frequency bands described above is needed.
It is thus necessary that, in order to respond to needs for further miniaturization of a wireless communication apparatus such as a mobile phone and for operations in a multi-band of frequencies, despite a tendency of an increase in antenna components, the antenna device can achieve its miniaturization and can have high performance.
An example of such a conventional antenna device embedded in one mobile phone being a wireless communication apparatus which uses a plurality of transmitting and receiving frequency bands is disclosed in Patent Reference 1 (Japanese Patent Application Laid-open No. 2004-88218) in which antennas each operating in every different transmitting and receiving band to be used is embedded in an antenna device of a mobile phone and these antennas are connected to one power feeding port in a branched manner to be mounted in a substrate (this technology is referred to as a conventional example).
However, such a conventional antenna device has problems. That is, the conventional antenna device generally does not use mutually and electromagnetically each of components making up the antenna device, in order words, the conventional antenna device arranges antennas in a manner being apart from one another so as to decrease mutual interference among antennas. Furthermore, in the conventional antenna device, power is fed to every antenna corresponding to each transmitting and receiving frequency band and, therefore, antenna switches are required, which causes the antenna circuit on the circuit to occupy space in the antenna device area.
There are conventional antenna devices in which one antenna is configured to handle signals in the IDCS band (1700 MHz), PCS band (1800 MHz), GSM band (900 MHz), and UMTS band (2200 MHz) in a shared manner to allot transmitting and receiving signals in the above GSM and UMTS bands to each transmitting and receiving circuit by using antenna switches.
However, the antenna switches used in the conventional antenna device to allot signals have complicated configurations and large insertion loss occurs in the UMTS band of high frequencies in particular.
Moreover, the above conventional antenna device presents another problem in that signals in all the DCS, PCS, GMC, and UMTS bands are handled in a shared manner using a single power feeding port, a deviation occurs in diffusion of radio waves, causing non-uniformity of directivity of vertically polarized waves in the antenna corresponding to each of the transmitting and receiving frequency bands.
Moreover, when these antennas are applied to a wireless communication apparatus such as a mobile phone, antenna switches to switch the transmitting and receiving frequency band are required, which occupies space for the antenna device on the substrate and, as a result, a degree of freedom of arrangement (layout) of the antenna in a cabinet of the wireless communication apparatus is decreased, which makes it difficult to miniaturize the wireless communication apparatus such as a mobile phone.
Furthermore, the conventional antenna device also has another problem in that, though easy impedance matching in a plurality of transmitting and receiving frequency bands is expected by mounting a main antenna on a substrate without using an antenna switch and by making a sub-antenna be branched from an intermediate position of the main antenna, problems of being unable to maintain non-directivity of vertically polarized waves of an antenna corresponding to each transmitting and receiving frequency band in a triple band including the GSM, DCS, and PCS bands and in a quad band including the GSM, DCS, PCS, and UMTS bands and being unable to stop a decrease in insertion loss and of being unable to save space remain still unsolved.